1. Field of the Invention
The present invention relates to a trench type power transistor device and a method of fabricating the same, and more particularly, to a trench type power transistor device having a low input resistance of a gate and a method of fabricating the same.
2. Description of the Prior Art
Power transistor devices are mainly applied to power management devices, such as switching power supplies, power management integrated circuits for computers or computer accessories, backlight power supplies and motor control devices, etc., and can be sorted as metal-oxide-semiconductor thin film transistor (MOSFET) devices and insulated gate bipolar transistor (IGBT) devices, etc. In general, the power transistor devices are designed with trenches to lower power consumptions.
In the trench type power transistor device, a gate conductive layer is disposed in a plurality of trenches of a substrate, and a doped body region is disposed in the substrate at sides of the trenches. Furthermore, a source region is disposed in the doped body region, so that a channel is vertically formed between the source region and the substrate. As we can see that a channel width of the trench type power transistor device is depended on the number of the trenches, and an on-resistance (Ron) of the trench type transistor power transistor device is depended on the channel width. Thus, the number of the trenches can be increased to augment the on-resistance. In addition, a source metal layer used for electrically connecting the source region to the outside is disposed in an active region, and a gate metal layer used for electrically connecting the gate conductive layer to the outside is disposed in a peripheral region surrounding the active region. Generally, the gate conductive layer is electrically connected to the gate metal layer by extending the trenches to the peripheral region, and the gate metal layer can be directly disposed on the gate conductive layer.
However, a size of the trench type power transistor device is generally fixed, so that a width of each trench is reduced when the number of the trenches is increased. However, since the widths of the trenches are reduced, a quantity of the gate conductive layer filling into the trenches is reduced, and a resistance between the gate conductive layer at the middle of each trench and the gate metal layer is increased. The input resistance of the gate of the trench type power transistor device is accordingly raised, and a delay time of resistive-capacitive delay is also increased.
As a result, to reduce an input resistance of the gate of the trench type power transistor device when the widths of the trenches are reduced is an important objective in this industry.